An oxidized metabolite of linoleic acid increases intracellular calcium in rat adrenal glomerulosa cells

Abstract

EKODE, an epoxy-keto derivative of linoleic acid, was previously shown to stimulate aldosterone secretion in rat adrenal glomerulosa cells ( 15 ). In the present study, we investigated the effect of exogenous EKODE on cytosolic [Ca2+] increase and aimed to elucidate the mechanism involved in this process. Through the use of the fluorescent Ca2+-sensitive dye Fluo-4, EKODE was shown to rapidly increase intracellular [Ca2+] ([Ca2+]i) along a bell-shaped dose-response relationship with a maximum peak at 5 μM. Experiments performed in the presence or absence of Ca2+revealed that this increase in [Ca2+]ioriginated exclusively from intracellular pools. EKODE-induced [Ca2+]iincrease was blunted by prior application of angiotensin II, Xestospongin C, and cyclopiazonic acid, indicating that inositol trisphosphate (InsP3)-sensitive Ca2+stores can be mobilized by EKODE despite the absence of InsP3production. Accordingly, EKODE response was not sensitive to the phospholipase C inhibitor U-73122. EKODE mobilized a Ca2+store included in the thapsigargin (TG)-sensitive stores, although the interaction between EKODE and TG appears complex, since EKODE added at the plateau response of TG induced a rapid drop in [Ca2+]i. 9-Oxo-octadecadienoic acid, another oxidized derivative of linoleic acid, also increases [Ca2+]i, with a dose-response curve similar to EKODE. However, arachidonic and linoleic acids at 10 μM failed to increase [Ca2+]ibut did reduce the amplitude of the response to EKODE. It is concluded that EKODE mobilizes Ca2+from an InsP3-sensitive store and that this [Ca2+]iincrease is responsible for aldosterone secretion by glomerulosa cells. Similar bell-shaped dose-response curves for aldosterone and [Ca2+]iincreases reinforce this hypothesis.